FR: support environment variables in (favourite) queries

Inizia individuando la gestione delle query preferite di litecli e il punto di ingresso per i comandi \f; l’issue non indica alcun file sorgente o test. Leggi come vengono sostituiti gli argomenti $1/$2 esistenti, poi chiarisci se l’espansione dell’ambiente si applica solo alle query preferite o a tutte le query. Il lavoro è completo quando la sintassi concordata funziona con le varianti di database illustrate senza rompere i parametri di query esistenti.

I'd love to see support for using environment variables in favourite queries, or even in all queries.

The use case is that I have several very similar databases where favourite queries all need to take a parameter to indicate what 'variant' of the database I'm currently using, or I have to copy configuration files for each database file and alter one value in each query filter.

Say, the different values are 'foo' and 'bar', and I have to either do:

favquery1 = '''select ...
    from some_table
    where parameter='$1'
    and other_paramater='$2'
'''
favquery2 = '''select ...
    from some_other_table sot inner join a_third_table att on sot.id = att.sot_id
    where sot.parameter='$1'
    and att.column_name ='$2'
'''

and then run \f favquery1 foo 42 and \f favquery2 bar 45, or I copy the configuration file multiple times and hardcode the parameter in each.

If, instead, I could use environment variables (syntax suggestion, feel free to come up with better syntax, this is based on bash):

favquery1 = '''select ...
    from some_table
    where parameter='${PARAMETER}'
    and other_paramater='$1'
'''
favquery2 = '''select ...
    from some_other_table sot inner join a_third_table att on sot.id = att.sot_id
    where sot.parameter='${PARAMETER}'
    and att.column_name ='$1'
'''

and then start each litecli instance with a different environment variable and use the exact same favourites for each database:

$ PARAMETER=foo litecli foo_database.sqlite
foo_database.sqlite> \f favquery1 42

and

$ PARAMETER=bar litecli bar_database.sqlite
bar_database.sqlite> \f favquery1 42